This application claims benefit of Japanese Patent Application No. 2001-116749 filed on Apr. 16, 2001, the contents of which are incorporated by the reference.
The present invention relates to array waveguide gratings used as light wavelength multiplexing/demultiplexing elements for optical communication, array waveguide grating modules, optical communication units and optical communication systems using the same array wavelength lattices. More specifically, the present invention concerns array waveguide gratings with improved light signal frequency characteristics, array waveguide modules, optical communication units and optical communication systems using the same array waveguide gratings.
With processes of usual time internet connection and communication data capacity increase, demands for large capacity data transfer are increasing. In the optical communication using light signals, it is very important for large capacity data transfer to improve the degree of wavelength multiplexing. In this respect, the role of array waveguide gratings as multiplexing/demultiplexing elements for multiplexing and demultiplexing light wavelengths is important, and the array waveguide gratings are thought to be one of key devices. The array waveguide grating has a passive structure, and also has a narrow light wavelength transmission width and a high extinction ratio. The array waveguide grating also has such features as that it can multiplex and demultiplex a number of light signals in correspondence to the number of waveguides.
Such array waveguide grating is desirably free from sudden changes of its output level or loss level with variations of the laser output light signal frequency from the center optical frequency of each optical waveguide. Also, where multiple stages of array waveguide gratings are connected, the modulation components of the light signal are cut off outside a bandwidth, in which the individual array waveguide gratings commonly transmit the light signal. Thus, it is important from the standpoint of improving the light signal transmission efficiency as well to realize a transmission characteristic with a flat peak level with respect to optical frequency.
FIG. 33 shows an example of such array waveguide grating. The illustrated array waveguide grating 10 has a substrate 11, on which one or more first channel waveguides (i.e., input channel waveguides) 12, a plurality of second channel waveguides (i.e., output channel waveguides) 13, a channel waveguide array 14 with a plurality of component channel waveguides bent in a predetermined direction with different radii of curvature, a first sector-shape slab waveguide 15 connecting the first channel waveguides 12 and the channel waveguide array 14 to one another and a second sector-shape slab waveguide 16 connecting the channel waveguide array 14 and the second channel waveguides 13 to one another, are formed. Multiplexed light signals with wavelengths xcex1 to xcexn, are incident from the first channel waveguides 12 on the first sector-shape slab waveguide 15, then proceed with their paths expanded therethough and are then incident on the channel waveguide array 14.
In the channel waveguide array 14, the component array waveguides have progressively increasing or reducing optical path lengths with a predetermined optical path length difference provided between adjacent ones of them. Thus, the light beams proceeding through the individual array waveguides reach the second sector-shape slab waveguide 16 with a predetermined phase difference provided between adjacent ones of them. Actually, wavelength dispersion takes place, and the in-phase plane is inclined in dependence on the wavelength. Consequently, the light beams are focused (i.e., converged) on the boundary surface between the second sector-shape slab waveguide 16 and the plurality of second channel waveguides 13 at positions different with wavelengths. The second channel waveguides 13 are disposed at positions corresponding to their respective wavelengths. Given wavelength components xcex1 to xcexn thus can be taken out independently from the second channel waveguides 13.
FIG. 34 shows, to an enlarged scale, a boundary part between the first channel waveguides and the first sector-shape slab waveguide in the array waveguide grating shown in FIG. 33. The first channel waveguides 121 to 123, which are shown in a first boundary part 18 shown in FIG. 33 as well, have optical waveguides 211 to 213 having a rectangular shape with a width Wp and length L2 and terminating in the first sector-shape slab waveguide 15.
FIG. 35 shows a boundary part in the case of using parabolic or second degree function shape waveguides disclosed in Japanese Patent Laid-Open No. 9-297228. In this case, the first channel waveguides 121 to 123 shown in the first boundary part 18 have optical waveguides 221 to 223 having a second degree function shape with a length L2 and terminating with a width Wp in the sector-shape slab waveguide 15.
Insertion loss and transmission width are usually in a trade-off relation to each other. However, where rectangular optical waveguides 211 to 213 shown in FIG. 34 are used in lieu of the second degree function shape light waveguides 221 to 223 shown in FIG. 35, the transmission width can be improved without sacrifice in the insertion loss. It is thus a great merit to use the rectangular optical waveguides 211 to 213 shown in FIG. 34 for realizing a flat transmitted light frequency characteristic.
The above description has concerned with the shapes of the optical waveguides, which are disposed in the first boundary part 18 between the first channel waveguide 12 and the first sector-shape slab waveguide 15 shown in FIG. 33. Such optical waveguides 21 and 22 are provided for the purpose of providing for harmonic mode of input at their locality of contact with the slab waveguide to make the Gaussian waveform peak part as flat as possible.
In lieu of providing the above contrivance with respect to the optical waveguides 21 and 22, the same effects are obtainable by providing optical waveguides of the same shapes in the second boundary part 19 as the boundary between the second channel waveguides 13 and the second sector-shape slab waveguide 16. Here, for the sake of the simplicity of description, only the shapes of the optical waveguides in the first boundary part 18 will be considered.
Where the rectangular optical waveguides 211 to 213 as shown in FIG. 34 are used, the variable shape parameters are only the width Wp and the length L2 of the rectangular part. Therefore, if the width Wp and the length L2 can assume only values limited on the design, it is possible to change the characteristics in such ranges. In other words, in this case a problem is posed that the degree of freedom in fine adjustment and fine design for realizing various properties is very low. For example, the problem may concern the transmission width and the stroke in the trade-off relation to each other. These problems will be discussed in detail in the following.
FIG. 36 shows an ideal characteristic of wavelength multiplexed light signals. In the graph, the ordinate is taken for the transmitted light signal power level, and the abscissa is taken for the wavelength. The individual light signals 311, 312, 313 have a rectangular waveform and also have a maximum transmission width. Thus, signal components of other light signals are not mixed with the signal components of the intrinsic light signals. Where such ideal light signals 311 to 313 are multiplexed, by connecting multiple stages of array waveguide gratings or array waveguide grating modules the bandwidth of the individual light signals is not reduced. The center wavelength of the light signals 311 to 313 may be deviated, but the signal level is not varied. However, no light signal transmitted through such array waveguide grating has such ideal rectangular waveform.
FIG. 37 shows a summary of proposal of an array waveguide grating with a rectangular optical waveguide connected to a slab waveguide. In the Figure, parts like those in FIG. 33 are designated by like reference numerals and symbols. In this proposal, first channel waveguide 12 and first sector-shape slab waveguide 15 are connected to each other by a rectangular waveguide 33.
FIG. 38 shows a way of use of the array waveguide grating shown in FIG. 37 such that multiplexed light signal is spread as it is led from channel waveguide through rectangular optical waveguide and then taken out as light signals each separated for each wavelength. As a light signal 32 passes through a rectangular optical waveguide,33, it is changed to a harmonic mode light signal 34 and spread. The spread light signal is converged through a channel waveguide array 14 and at positions each peculiar for each wavelength. The converged light signal 37 is separated and taken out for each wavelength in such a form as to correspond to the position of a second channel waveguide 13.
FIG. 39 shows optical frequency characteristics of light signals taken out in the example shown in FIG. 38. As shown, individual light signals 37 are multiplexed with a high density, and skirt portions of adjacent light signals and also skirt portions of light signals at spaced-apart positions are complicatedly intrude in the wavelength ranges of intrinsic light signals.
FIG. 40 shows light signals of two adjacent channels. Light signals 331 and 332 shown by solid curves have a smaller transmission width T as shown by arrows than the case of light signals 341 and 342 shown by broken lines, but the influence of noise components due to cross-talk is less. However, the light signals 331 and 332 are sharper in waveform than the light signals 341 and 342, and therefore they are subject to greater loss in the case of deviation from the center wavelength. As shown, the optical frequency characteristic varies with the light signal waveform shape. For this reason, when building a communication system, it is necessary to determine the optical frequency characteristic of the array waveguide grating or the array waveguide grating module on ,the basis of a desire of giving preference to the transmission width or attaching importance to the cross-talk. For example, in the case of a trunk communication system it is possible that light signal is relayed at many places as it is transferred, and it is thought to attach importance to the cross-talk for minimizing the deterioration of signal. In the case of a terminal communication system, on the other hand, simpler circuit devices than those in the trunk system are used. In this circumstance, a certain extent of deviation from the center wavelength of each signal channel has to be allowed. In this case, importance thus may be attached to the transmission width.
Thus, as described before, with the rectangular optical waveguides 211 to 213 as shown in FIG. 34 the degree of freedom of changing the optical frequency characteristics in dependence on the circumstance with the array waveguide grating used therein is low. In this respect, the optical waveguides 221 to 223 having the second degree function shape as shown in FIG. 35 become attractive.
However, the wavelength multiplexing degree improvement demand is on a trend of being increased more and more. When the channel width of each light signal is correspondingly reduced, the gap width between the signal transmission widths of adjacent channel light signals are relatively reduced to strengthen the degree of inter-channel interference, thus resulting in relative cross-talk deterioration. In this situation, it is difficult to manufacture array waveguide gratings or array waveguide grating modules, which permit satisfactorily setting transmission width and cross-talk for meeting demands for various communication systems.
An object of the present invention, therefore, is to provide array waveguide gratings, array waveguide grating modules and optical communication systems capable of increasing the degree of freedom of optical frequency characteristics and obtaining transmitted light of flatter characteristics than in the case where second degree function shape optical waveguides are used for connecting channel waveguide and slab waveguide to one another.
According to a first aspect of the present invention, there is provided an array waveguide grating comprising: a predetermined substrate; a first and a second channel waveguide for light wave transfer on the substrate; a channel waveguide array having a plurality of component waveguides having lengths progressively increasing with a predetermined difference between adjacent ones of the waveguides on the substrate; a first slab waveguide for connecting the ends of the first channel waveguides and one end of the channel waveguide array via a waveguide part having a first shape on the substrate; and a second slab waveguide for connecting one end of the second channel waveguides and the other end of the channel waveguide array via a waveguide part having a second shape on the substrate; wherein: at least the open part of each of the first channel waveguides on the side of the first slab waveguide or the open part of each of the second channel waveguides on the side of the second slab waveguide is flaring in an exponential function shape toward the channel waveguide array.
According to a second aspect of the present invention, there is provided an array waveguide grating comprising: a predetermined substrate; a first and a second channel waveguide for light wave transfer on the substrate; a channel waveguide array having a plurality of component waveguides having lengths progressively increasing with a predetermined difference between adjacent ones of the waveguides on the substrate; a first slab waveguide for connecting the ends of the first channel waveguides and one end of the channel waveguide array via a waveguide part having a first shape on the substrate; and a second slab waveguide for connecting one end of the second channel waveguides and the other end of the channel waveguide array via a waveguide part having a second shape on the substrate; wherein: at least a part of at least the open part of each of the first channel waveguides on the side of the first slab waveguide or the open part of each of the second channel waveguides on the side of the second slab waveguide is flaring in an exponential function shape toward the channel waveguide array.
In a third aspect of the present invention according to the first or second aspect, the shape W(X) flaring in the exponential function shape is represented as
W(X)=(Wpxe2x88x92Wc)*(1xe2x88x92exp(xe2x88x92a*X))+Wc
where X represents the light wave progress direction, Wp is the width of the end of the shape connected to the slab waveguide, Wc is the spread of the waveguide part in directions perpendicular to the light wave progress direction X, and a represents a parameter (i.e., shape variable) giving the exponential function shape.
In a fourth aspect of the present invention according to the third aspect, wherein the shape variable a giving the exponential function shape is unity or below.
In a fifth aspect of the present invention according to the third aspect, both of the first and second shape waveguide parts have a shape part flaring from in an exponential function shape from the side of the channel waveguides toward the channel waveguide array and are different in the value of the shape variable a from each other.
In a sixth aspect of the present invention according to the third aspect, at least either the open part of each of the first channel waveguides on the side of the first slab waveguide or the open part of each of the second channel waveguides on the side of the second slab waveguide has a shape part flaring in an exponential function shape toward the channel waveguide array, and the value of the shape variable a is set independently to a value corresponding to a corresponding channel waveguide.
In a seventh aspect of the present invention according to the second aspect, wherein parts of the first and second shape waveguide parts which do not have any shape part flaring in the exponential function shape have a taper shape.
In an eighth aspect of the present invention according to the second aspect, parts of the first and second shape waveguide parts which do not have any shape part flaring in the exponential function shape have a second degree function shape.
In a ninth aspect of the present invention according to the second aspect, parts of the first and second shape waveguide parts which do not have any shape part flaring in the exponential function shape have both a taper shape and a second degree function shape. In a tenth aspect of the present invention according to the second aspect, the other shapes in the case of a part containing a shape part flaring in the exponential function shape consist of a taper shape part. In an eleventh aspect of the present invention according to the second aspect, the other shapes in the case of a part containing a shape part flaring in the exponential function shape consist of a second degree function shape part.
In a twelfth aspect of the present invention according to the second aspect, the other shapes in the case of a part containing a shape part flaring in the exponential function shape consist of a taper shape part and a second degree function shape part.
According to a thirteenth aspect of the present invention, there is provided an array waveguide grating comprising: a predetermined substrate; a first and a second channel waveguide for light wave transfer on the substrate; a channel waveguide array having a plurality of component waveguides having lengths progressively increasing with a predetermined difference between adjacent ones of the waveguides on the substrate; a first slab waveguide for connecting the ends of the first channel waveguides and one end of the channel waveguide array via a waveguide part having a first shape on the substrate; and a second slab waveguide for connecting one end of the second channel waveguides and the other end of the channel waveguide array via a waveguide part having a second shape on the substrate; wherein: at least the open part of each of the first channel waveguides on the side of the first slab waveguide or the open part of each of the second channel waveguides with respect to the second slab waveguide has a shape part flaring in an exponential function shape represented by a function of a degree higher than the second degree toward the channel waveguide array.
According to a fourteenth aspect of the present invention, there is provided an array waveguide grating comprising: first and second channel waveguides for light wave transfer; a channel waveguide array having a plurality of component waveguides having lengths progressively increasing with a predetermined difference between adjacent ones of the waveguides; a first slab waveguide disposed between the first channel waveguides and one end of the channel waveguide array; and a second slab waveguide disposed between the second channel waveguides and the other end of the channel waveguide array; wherein: at least the open part of each of the first channel waveguides on the side of the first slab waveguide or the open part of each of the second channel waveguides on the side of the second slab waveguide has an open end with an opening width greater than the waveguide width of the first or second channel waveguides; and the shape directed from the stem part of the open part toward the open end is found on the inner side of rectangular shape of the opening width and on the outer side of a second degree curve connecting the stem part and the open end.
In a fifteenth aspect of the present invention according to the thirteenth aspect, the flaring shape part represented by the function of a degree higher than the second degree has such a convex shape that when frequency multiplexed Gaussian waveform light waves pass through their waveguides, their characteristics line in a rage between boundary ranges of characteristics with respect to the transmission width and the cross-talk when they pass through the rectangular waveguides and second degree function shape waveguides.
According to a sixteenth aspect of the present invention, there is provided an array waveguide grating module comprising; an array waveguide grating including a predetermined substrate, a first and a second channel waveguide for light wave transfer on the substrate, a channel waveguide array having a plurality of component waveguides having lengths progressively increasing with a predetermined difference between adjacent ones of the waveguides on the substrate, a first slab waveguide for connecting the ends of the first channel waveguides and one end of the channel waveguide array via a waveguide part having a first shape on the substrate, and a second slab waveguide for connecting one end of the second channel waveguides and the other end of the channel waveguide array via a waveguide part having a second shape on the substrate, wherein at least the open part of each of the first channel waveguides on the side of the first slab waveguide or the open part of each of the second channel waveguides on the side of the second slab waveguide is flaring in an exponential function shape toward the channel waveguide array; and an optical fiber having one end optically connected to at least part of the first or second channel waveguides of the array waveguide grating.
According to a seventeenth aspect of the present inventions there is provided an array waveguide grating module comprising: an array waveguide grating including a predetermined substrate, a first and a second channel waveguide for light wave transfer on the substrate, a channel waveguide array having a plurality of component waveguides having lengths progressively increasing with a predetermined difference between adjacent ones of the waveguides on the substrate, a first slab waveguide for connecting the ends of the first channel waveguides and one end of the channel waveguide array via a waveguide part having a first shape on the substrate, and a second slab waveguide for connecting one end of the second channel waveguides and the other end of the channel waveguide array via a waveguide part having a second shape on the substrate; wherein at least a part of at least the open part of each of the first channel waveguides on the side of the first slab waveguide or the open part of each of the second channel waveguides on the side of the second slab waveguide is flaring in an exponential function shape toward the channel waveguide array; and an optical fiber having one end optically connected to at least part of the first or second channel waveguides of the array waveguide grating.
According to an eighteenth aspect of the present invention, there is provided an array waveguide grating module comprising; an array waveguide grating including first and second channel waveguides for light wave transfer, a channel waveguide array having a plurality of component waveguides having lengths progressively increasing with a predetermined difference between adjacent ones of the waveguides, a first slab waveguide disposed between the first channel waveguides and one end of the channel waveguide array and a second slab waveguide disposed between the second channel waveguides and the other end of the channel waveguide array, wherein at least the open part of each of the first channel waveguides on the side of the first slab waveguide or the open part of each of the second channel waveguides on the side of the second slab waveguide has an open end with an opening width greater than the waveguide width of the first or second channel waveguides, and the shape directed from the stem part of the open part toward the open end is found on the inner side of rectangular shape of the opening width and on the outer side of a second degree curve connecting the stem part and the open end; and an optical fiber having one end optically connected to at least part of the first or second channel waveguides of the array waveguide grating.
In a nineteenth aspect of the present invention according to the sixteenth or seventeenth aspect, the shape W(X) flaring in the exponential function shape is represented as
W(X)=(Wpxe2x88x92Wc)*(1xe2x88x92exp(xe2x88x92a*X))+Wc
where X represents the light wave progress direction, Wp is the width of the end of the shape connected to the slab waveguide, Wc is the spread of the waveguide part in directions perpendicular to the light wave progress direction X, and a represents a parameter (i.e., shape variable) giving the exponential function shape.
In a twentieth aspect of the present invention according to the nineteenth aspect, the shape variable a giving the exponential function shape is unity or below.
In a twenty-first aspect of the present invention according to the nineteenth aspect, both of the first and second shape waveguide parts have a shape part flaring from in an exponential function shape from the side of the channel waveguides toward the channel waveguide array and are different in the value of the shape variable a from each other.
In a twenty-second aspect of the present invention according to the nineteenth aspect, at least either the open part of each of the first channel waveguides on the side of the first slab waveguide or the open part of each of the second channel waveguides on the side of the second slab waveguide has a shape part flaring in an exponential function shape toward the channel waveguide array, and the value of the shape variable a is set independently to a value corresponding to a corresponding channel waveguide.
In a twenty-third aspect of the present invention according to the sixteenth or seventeenth aspect, parts of the first and second shape waveguide parts which do not have any shape part flaring in the exponential function shape have a taper shape.
In a twenty-fourth aspect of the present invention according to the sixteenth or seventeenth aspect, parts of the first and second shape waveguide parts which do not have any shape part flaring in the exponential function shape have a second degree function shape.
In a twenty-fifth aspect of the present invention according to the sixteenth or seventeenth aspect, parts of the first and second shape waveguide parts which do not have any shape part flaring in the exponential function shape have both a taper shape and a second degree function shape.
In a twenty-sixth aspect of the present invention according to the seventeenth aspect, the other shapes in the case of a part containing a shape part flaring in the exponential function shape consist of a taper shape part.
In a twenty-seventh aspect of the present invention according to the seventeenth aspect, the other shapes in the case of a part containing a shape part flaring in the exponential function shape consist of a second degree function shape part.
In a twenty-eighth aspect of the present invention according to the seventeenth aspect, the other shapes in the case of a part containing a shape part flaring in the exponential function shape consist of a taper shape part and a second degree function shape part.
In a twenty-ninth aspect of the present invention, there is provided an array waveguide grating module comprising: an array waveguide grating including a predetermined substrate, a first and a second channel waveguide for light wave transfer on the substrate, a channel waveguide array having a plurality of component waveguides having lengths progressively increasing with a predetermined difference between adjacent ones of the waveguides on the substrate, a first slab waveguide for connecting the ends of the first channel waveguides and one end of the channel waveguide array via a waveguide part having a first shape on the substrate, and a second slab waveguide for connecting one end of the second channel waveguides and the other end of the channel waveguide array via a waveguide part having a second shape on the substrate, wherein at least the open part of each of the first channel waveguides on the side of the first slab waveguide or the open part of each of the second channel waveguides with respect to the second slab waveguide has a shape part flaring in an exponential function shape represented by a function of a degree higher than the second degree toward the channel waveguide array; and an optical fiber having one end optically connected to at least part of the first or second channel waveguides of the array waveguide grating.
In a thirty aspect of the present invention according to the twenty-ninth aspect, the flaring shape part represented by the function of a degree higher than the second degree has such a convex shape that when frequency multiplexed Gaussian waveform light waves pass through their waveguides, their characteristics line in a rage between boundary ranges of characteristics with respect to the transmission width and the cross-talk when they pass through the rectangular waveguides and second degree function shape waveguides.
According to a thirty-first aspect of the present invention, there is provided an optical communication system comprising: an optical transmission means for sending out light signals of different wavelengths as parallel signals; a multiplexer constituted by an array waveguide grating for wavelength multiplexing/demultiplexing each of the different wavelength light signals sent out from the optical transmission means; an optical transmission line, to which the wavelength divided and multiplexed light signals outputted from the multiplexer are sent; a node provided in the optical transmission line and having an array waveguide grating; a demultiplexer constituted by an array waveguide array for receiving input light signal set along the optical transmission line via the node; and an optical receiving means for receiving the demultiplexed different wavelength light signals from the demultiplexer; wherein the demultiplexer includes a predetermined substrate, a first and a second channel waveguide for light wave transfer on the substrate, a channel waveguide array having a plurality of component waveguides having lengths progressively increasing with a predetermined difference between adjacent ones of the waveguides on the substrate, a first slab waveguide for connecting the ends of the first channel waveguides and one end of the channel waveguide array via a waveguide part having a first shape on the substrate, and a second slab waveguide for connecting one end of the second channel waveguides and the other end of the channel waveguide array via a waveguide part having a second shape on the substrate, and at least the open part of each of the first channel waveguides on the side of the first slab waveguide or the open part of each of the second channel waveguides on the side of the second slab waveguide is flaring in an exponential function shape toward the channel waveguide array.
According to a thirty-second aspect of the present invention, there is provided an optical communication system comprising: an optical transmission means for sending out light signals of different wavelengths as parallel signals; a multiplexer constituted by an array waveguide grating for wavelength multiplexing/demultiplexing each of the different wavelength light signals sent out from the optical transmission means; an optical transmission line, to which the wavelength divided and multiplexed light signals outputted from the multiplexer are sent; a node provided in the optical transmission line and having an array waveguide grating; a demultiplexer constituted by an array waveguide array for receiving input light signal set along the optical transmission line via the node; and an optical receiving means for receiving the demultiplexed different wavelength light signals from the demultiplexer; wherein the demultiplexer includes a predetermined substrate, a first and a second channel waveguide for light wave transfer on the substrate, a channel waveguide array having a plurality of component waveguides having lengths progressively increasing with a predetermined difference between adjacent ones of the waveguides on the substrate, a first slab waveguide for connecting the ends of the first channel waveguides and one end of the channel waveguide array via a waveguide part having a first shape on the substrate, and a second slab waveguide for connecting one end of the second channel waveguides and the other end of the channel waveguide array via a waveguide part having a second shape on the substrate, and at least a part of at least the open part of each of the first channel waveguides on the side of the first slab waveguide or the open part of each of the second channel waveguides on the side of the second slab waveguide is flaring in an exponential function shape toward the channel waveguide array.
According to a thirty-third aspect of the present invention, there is provided an optical communication system comprising: an optical transmission means for sending out light signals of different wavelengths as parallel signals; a multiplexer constituted by an array waveguide grating for wavelength multiplexing/demultiplexing each of the different wavelength light signals sent out from the optical transmission means; an optical transmission line, to which the wavelength divided and multiplexed light signals outputted from the multiplexer are sent; a node provided in the optical transmission line and having an array waveguide grating; a demultiplexer constituted by an array waveguide array for receiving input light signal set along the optical transmission line via the node; and an optical receiving means for receiving the demultiplexed different wavelength light signals from the demultiplexer; wherein the demultiplexer includes a predetermined substrate, a first and a second channel waveguide for light wave transfer on the substrate, a channel waveguide array having a plurality of component waveguides having lengths progressively increasing with a predetermined difference between adjacent ones of the waveguides on the substrate, a first slab waveguide for connecting the ends of the first channel waveguides and one end of the channel waveguide array via a waveguide part having a first shape on the substrate, and a second slab waveguide for connecting one end of the second channel waveguides and the other end of the channel waveguide array via a waveguide part having a second shape on the substrate, and includes at least the open part of each of the first channel waveguides on the side of the first slab waveguide or the open part of each of the second channel waveguides with respect to the second slab waveguide has a shape part flaring in an exponential function shape represented by a function of a degree higher than the second degree toward the channel waveguide array.
According to a thirty-fourth aspect of the present invention, there is provided an optical communication system comprising: an optical transmission means for sending out light signals of different wavelengths as parallel signals; a multiplexer constituted by an array waveguide grating for wavelength multiplexing/demultiplexing each of the different wavelength light signals sent out from the optical transmission means; an optical transmission line, to which the wavelength divided and multiplexed light signals outputted from the multiplexer are sent; a node provided in the optical transmission line and having an array waveguide grating; a demultiplexer constituted by an array waveguide array for receiving input light signal set along the optical transmission line via the node; and an optical receiving means for receiving the demultiplexed different wavelength light signals from the demultiplexer; wherein the demultiplexer including first and second channel waveguides for light wave transfer, a channel waveguide array having a plurality of component waveguides having lengths progressively increasing with a predetermined difference between adjacent ones of the waveguides, a first slab waveguide disposed between the first channel waveguides and one end of the channel waveguide array, and a second slab waveguide disposed between the second channel waveguides and the other end of the channel waveguide array, and at least the open part of each of the first channel waveguides on the side of the first slab waveguide or the open part of each of the second channel waveguides on the side of the second slab waveguide has an open end with an opening width greater than the waveguide width of the first or second channel waveguides, and the shape directed from the stem part of the open part toward the open end is found on the inner side of rectangular shape of the opening width and on the outer side of a second degree curve connecting the stem part and the open end.
In a thirty-fifth aspect of the present invention according to the thirty-third aspect, the flaring shape part represented by the function of a degree higher than the second degree has such a convex shape that when frequency multiplexed Gaussian waveform light waves pass through their waveguides, their characteristics line in a rage between boundary ranges of characteristics with respect to the transmission width and the cross-talk when they pass through the rectangular waveguides and second degree function shape waveguides.
According to a thirty-sixth aspect of the present invention, there is provided an optical communication system comprising a plurality of nodes connected by transfer lines into a loop form, wavelength multiplexed and demultiplexed light signals being transferred along the loop form transfer line, the nodes each including a first array waveguide grating for demultiplexing the multiplexed light signal into light signals of different wavelengths and a second array waveguide grating for multiplexing the demultiplexed light signals of the different wavelengths, wherein the first array waveguide grating includes a predetermined substrate, a first and a second channel waveguide for light wave transfer on the substrate, a channel waveguide array having a plurality of component waveguides having lengths progressively increasing with a predetermined difference between adjacent ones of the waveguides on the substrate, a first slab waveguide for connecting the ends of the first channel waveguides and one end of the channel waveguide array via a waveguide part having a first shape on the substrate, and a second slab waveguide for connecting one end of the second channel waveguides and the other end of the channel waveguide array via a waveguide part having a second shape on the substrate, and at least the open part of each of the first channel waveguides on the side of the first slab waveguide or the open part of each of the second channel waveguides on the side of the second slab waveguide is flaring in an exponential function shape toward the channel waveguide array.
According to a thirty-seventh aspect of the present invention, there is provided an optical communication system comprising a plurality of nodes connected by transfer lines into a loop form, wavelength multiplexed and demultiplexed light signals being transferred along the loop form transfer line, the nodes each including a first array waveguide grating for demultiplexing the multiplexed light signal into light signals of different wavelengths and a second array waveguide grating for multiplexing the demultiplexed light signals of the different wavelengths, wherein the first array waveguide grating includes a predetermined substrate, a first and a second channel waveguide for light wave transfer on the substrate, a channel waveguide array having a plurality of component waveguides having lengths progressively increasing with a predetermined difference between adjacent ones of the waveguides on the substrate, a first slab waveguide for connecting the ends of the first channel waveguides and one end of the channel waveguide array via a waveguide part having a first shape on the substrate, a second slab waveguide for connecting one end of the second channel waveguides and the other end of the channel waveguide array via a waveguide part having a second shape on the substrate, and at least a part of at least the open part of each of the first channel waveguides on the side of the first slab waveguide or the open part of each of the second channel waveguides on the side of the second slab waveguide is flaring in an exponential function shape toward the channel waveguide array.
According to a thirty-eighth aspect of the present invention, there is provided an optical communication system comprising a plurality of nodes connected by transfer lines into a loop form, wavelength multiplexed and demultiplexed light signals being transferred along the loop form transfer line, the nodes each including a first array waveguide grating for demultiplexing the multiplexed light signal into light signals of different wavelengths and a second array waveguide grating for multiplexing the demultiplexed light signals of the different wavelengths, wherein the first array waveguide grating includes a predetermined substrate, a first and a second channel waveguide for light wave transfer on the substrate, a channel waveguide array having a plurality of component waveguides having lengths progressively increasing with a predetermined difference between adjacent ones of the waveguides on the substrate, a first slab waveguide for connecting the ends of the first channel waveguides and one end of the channel waveguide array via a waveguide part having a first shape on the substrate, a second slab waveguide for connecting one end of the second channel waveguides and the other end of the channel waveguide array via a waveguide part having a second shape on the substrate, and at least the open part of each of the first channel waveguides on the side of the first slab waveguide or the open part of each of the second channel waveguides with respect to the second slab waveguide has a shape part flaring in an exponential function shape represented by a function of a degree higher than the second degree toward the channel waveguide array.
According to a thirty-ninth aspect of the present invention, there is provided an optical communication system comprising a plurality of nodes connected by transfer lines into a loop form, wavelength multiplexed and demultiplexed light signals being transferred along the loop form transfer line, the nodes each including a first array waveguide grating for demultiplexing the multiplexed light signal into light signals of different wavelengths and a second array waveguide grating for multiplexing the demultiplexed light signals of the different wavelengths, wherein the first array waveguide grating includes first and second channel waveguides for light wave transfer, a channel waveguide array having a plurality of component waveguides having lengths progressively increasing with a predetermined difference between adjacent ones of the waveguides, a first slab waveguide disposed between the first channel waveguides and one end of the channel waveguide array, a second slab waveguide disposed between the second channel waveguides and the other end of the channel waveguide array, at least the open part of each of the first channel waveguides on the side of the first slab waveguide or the open part of each of the second channel waveguides on the side of the second slab waveguide has an open end with an opening width greater than the waveguide width of the first or second channel waveguides, and the shape directed from the stem part of the open part toward the open end is found on the inner side of rectangular shape of the opening width and on the outer side of a second degree curve connecting the stem part and the open end.
In a fortieth aspect of the present invention according to the thirty-eighth aspect, the flaring shape part represented by the function of a degree higher than the second degree has such a convex shape that when frequency multiplexed Gaussian waveform light waves pass through their waveguides, their characteristics line in a rage between boundary ranges of characteristics with respect to the transmission width and the cross-talk when they pass through the rectangular waveguides and second degree function shape waveguides.
Other objects and features will be clarified from the following description with reference to attached drawings.